Wireless communication devices, which may typically be portable phones, have become widely used and there has been an increasing demand for miniaturized and lightweight resonators and filters using such resonators. Conventionally, a dielectric filter and a surface acoustic wave filter (SAW filter) are generally used. Recently, a piezoelectric thin-film resonator and a filer using such a resonator have been widely noticed because the piezoelectric thin-film resonator may be downsized and implemented monolithically.